1. Field of the Invention
The present invention relates to a constitution of a wide angle projection lens having a large image circle, which is mounted in a projection display device using a light valve, and a projection display device mounted with this wide angle projection lens.
2. Description of the Background Art
FIG. 17 is an illustration showing an eccentric projection optical system in a projection display device using a background-art reflection light valve. This figure shows an illumination luminous flux 91 illuminating a reflection light valve 6, a reflection luminous flux 92 reflected by the reflection light valve 6 and entering a projection lens 8 and an optical axis 93 of the projection lens 8.
The illumination light 91 is irradiated diagonally with respect to the reflection light valve 6, and the luminous flux 92 reflected by the reflection light valve 6, being two-dimensionally modulated in a surface of the reflection light valve 6, is enlargedly projected on a not-shown screen by the projection lens 8.
A display area of the reflection light valve 6 is perpendicular to the optical axis 93 of the projection lens 8 and disposed eccentrically with its center point displaced downward with respect to the lens optical axis 93. This is intended to avoid physical interference between an illumination optical system generating the illumination light 91 and the projection lens 8, prevent generation of eclipse of the illumination luminous flux or projection luminous flux and obtain a uniform projection image.
In order to dispose the reflection light valve 6 eccentrically with respect to the projection lens 8, as discussed above, it is necessary to enlarge the specifications on the image circle of the projection lens 8 (an area where the aberration of the projection lens 8 is well corrected). This situation will be discussed, referring to FIGS. 18A, 18B, 19A and 19B.
FIGS. 18A and 18B show image circles IMC of the projection lens 8 projecting the light valve 6 with aspect ratio of 4:3. Specifically, FIG. 18A shows a case where the center point of the light valve 6 coincides with the center point of the image circle IMC (on-axis projection) and FIG. 18B shows a case where the center point of the upper long side of the light valve 6 coincides with the center point of the image circle IMC (off-axis projection). It can be seen from these figures that the diameter of the image circle in the on-axis projection is 5 while that of the image circle in the off-axis projection is 7.2, being larger by 44%.
FIGS. 19A and 19B show image circles IMC of the projection lens 8 projecting the light valve 6 with aspect ratio of 16:9. Specifically, FIG. 19A shows a case where the center point of the light valve 6 coincides with the center point of the image circle IMC (on-axis projection) and FIG. 19B shows a case where the center point of the upper long side of the light valve 6 coincides with the center point of the image circle IMC (off-axis projection). It can be seen from these figures that the diameter of the image circle in the on-axis projection is 18.36 while that of the image circle in the off-axis projection is 24.08, being larger by about 31%.
Further, it is understood from the above examples that the diameter of the image circle becomes larger when the degree of eccentricity of the light valve 6 is larger.
Since the off-axis projection system has a simple constitution and a projection light corresponding to the center point of the screen can go out, being tilted upwards with respect to the optical axis 93 of the projection lens, there is a case where the off-axis projection system is adopted in a small-size front projection type projector. In this system, the image circle of the projection lens 8 becomes larger than the diagonal size of the light valve 6. This makes it difficult to realize both reduction in focal length required for size-reduction of a body incorporating the whole optical system and excellent imaging, especially in a case of applying the off-axis projection system to a rear projection type projector.
As a background-art example of projection lens for DMD (Digital Micromirror Device) projection, for instance, one disclosed in Japanese Patent Application Laid Open Gazette No. 2000-275729 is well known. This background-art example proposes a constitution of a projection lens with half angle of projection view xcfx89=27.3 degrees at F/3 with respect to the tilt angle of xc2x110 degrees of micromirrors constituting the DMD. This also discloses a lens constitution intended for reduction in interference between the illumination luminous flux and the projection luminous flux by disposing the stop of the whole lens system on the DMD side. Since an element having micromirrors with the tilt angle of xc2x112 degrees is being developed through the research and development of DMD, however, the specification of about F/2.4 is required for a projection lens in order to achieve a high-intensity projector while ensuring sufficient projection luminous flux. Further, the half angle of projection view of 27.3 degrees in the above example, which makes the projection distance with respect to a predetermined screen size too large in a rear projection type projector, has a problem in being used for a small-size rear projection type projector. It is desirable to ensure a half angle of view of 40 degrees or more for a projection lens.
Items of basic specification required for a projection lens of off-axis projection system used in a rear projection type display device are as follows.
(1) Wide angle of view: a projection lens with short focal length is needed in order to mount an optical system in a small-size body with the projection distance shortened. As discussed above, it is desirable that the half angle of view xcfx89 of lens greater than 40 degrees at F/2.4.
(2) Small diameter of a lens on the incident side: it is desired that the diameter of a projection lens on the incident side of the luminous flux (light valve side) should be as small as possible in order to avoid luminous flux eclipse caused by interference between the illumination optical system and the projection optical system.
(3) Long back focal length: combined with the requirement (2), it is required that the back focal length on the light valve side should be set longer in order to avoid luminous flux eclipse caused by the interference between the illumination optical system and the projection optical system.
(4) Large image circle: required is a lens system with aberration well corrected in a large image circle in order to be used for the off-axis projection.
In the rear projection type display device required is a projection lens further having the following fundamental properties besides satisfying the above basic specifications relating to (1) wide angle of view, (2) small diameter of a lens on the incident side, (3) long back focal length and (4) large image circle.
(a) Low chromatic aberration: it is needed to control the chromatic difference of magnification, typically to about pixel-pitch level, or desirably to half the pixel-pitch level or lower in order to sufficiently reduce the difference in projection magnification among primary color pixels of a projection image, and it is further needed to control the longitudinal chromatic aberration to be smaller so that the focuses of primary colors may coincide with one another.
(b) Low distortion aberration: it is required that a projection lens should be designed to control the displacement of pixel off from an ideal point due to distortion aberration typically to about 1% or lower since distortions at peripheral portions in a screen are visible as a rectangular projection image is projected inside a frame of a projection screen in a rear projection type projector.
(c) High resolution: in order to enlargedly project an original image of a high-density and multipixel light valve element having million-level pixels which has been increasingly developed in recent years, a projection lens of high resolution corresponding to a fine pixel structure of the light valve is required, and further in order to ensure high resolution of the projection lens, it is needed to sufficiently correct on-axis aberrations and off-axis aberrations other than the above-discussed chromatic aberration and distortion aberration.
The present invention is directed to a wide angle projection lens. According to a first aspect of the present invention, the wide angle projection lens comprises a Gnp lens group having positive refractive power and a Gf lens group having positive refractive power in the order from a large conjugate side toward a small conjugate side, the Gnp lens group comprises a Gn lens group having negative refractive power and a Gp lens group having positive refractive power in the order from a large conjugate side toward a small conjugate side, and the wide angle projection lens satisfies relations of the following expressions (1), (2), (3) and (4).
xe2x88x921.8 less than fn/f less than xe2x88x921.1xe2x80x83xe2x80x83(1)
3.2 less than fp/f less than 5.5xe2x80x83xe2x80x83(2)
1.2 less than Dnp/f less than 2.4xe2x80x83xe2x80x83(3)
2.8 less than ff/fnp less than 4.4xe2x80x83xe2x80x83(4)
where
f: focal length of the whole lens system
fn: focal length of the Gn lens group
fp: focal length of the Gp lens group
Dnp: air spacing between the Gn lens group and the Gp lens group
fnp: focal length of the Gnp lens group
ff: focal length of the Gf lens group.
According to a second aspect of the present invention, the wide angle projection lens of the first aspect satisfies a relation of the following expression (5).
3.0 less than BFLnp/fnp less than 4.5xe2x80x83xe2x80x83(5)
where
fnp: focal length of the Gnp lens group
BFLnp: back focal length of the Gnp lens group.
According to a third aspect of the present invention, the wide angle projection lens of the first aspect satisfies a relation of the following expression (6).
|EXPnp|/fnp less than 2.0xe2x80x83xe2x80x83(6)
where
fnp: focal length of the Gnp lens group
|EXPnp|: absolute value of pupil distance on the small conjugate side of the Gnp lens group viewed from the last surface on the small conjugate side.
According to a fourth aspect of the present invention, the wide angle projection lens of the first aspect satisfies a relation of the following expression (7).
0.6 less than Dpf/ff less than 1.2xe2x80x83xe2x80x83(7)
where
ff: focal length of the Gf lens group
Dpf: air spacing between the Gp lens group and the Gf lens group.
According to a fifth aspect of the present invention, the wide angle projection lens of the first aspect satisfies a relation of the following expression (8).
0.75 less than (Dpfxe2x88x92EXPnp)/ff less than 1.5xe2x80x83xe2x80x83(8)
where
ff: focal length of the Gf lens group
Dpf: air spacing between the Gp lens group and the Gf lens group
EXPnp: pupil distance on the small conjugate side of the Gnp lens group viewed from the last surface on the small conjugate side.
According to a sixth aspect of the present invention, in the wide angle projection lens of the first aspect, the Gn lens group comprises a Gn1 lens group having negative refractive power and a Gn2 lens group having negative refractive power in the order from the large conjugate side toward the small conjugate side, and the Gp lens group comprises a Gp1 lens group having positive refractive power and a Gp2 lens group having positive refractive power in the order from the large conjugate side toward the small conjugate side.
According to a seventh aspect of the present invention, in the wide angle projection lens of the sixth aspect, the Gn1 lens group comprises a first lens which is a meniscus lens with a convex surface on the large conjugate side, having negative refractive power; a second lens which is a meniscus lens with a convex surface on the large conjugate side, having negative refractive power; a third lens which is a biconvex lens having positive refractive power; a fourth lens which is a meniscus lens with a convex surface on the large conjugate side, having negative refractive power; and a fifth lens which is a biconcave lens having negative refractive power in the order from the large conjugate side toward the small conjugate side, the Gn2 lens group comprises a sixth lens which is a biconvex lens having positive refractive power; and a seventh lens with a concave surface on the small conjugate side, having negative refractive power in the order from the large conjugate side toward the small conjugate side, and the Gp1 lens group comprises an eighth lens with a convex surface on the large conjugate side, having positive refractive power; a ninth lens which is a meniscus lens with a convex surface on the small conjugate side, having positive refractive power; a tenth lens which is a biconcave lens having negative refractive power; and an eleventh lens which is a biconvex lens having positive refractive power and connected to the tenth lens.
According to an eighth aspect of the present invention, in the wide angle projection lens of the sixth aspect, the Gp2 lens group includes at least one aspheric surface.
According to a ninth aspect of the present invention, in the wide angle projection lens of the sixth aspect, the Gp2 lens group includes stop means.
According to a tenth aspect of the present invention, in the wide angle projection lens of the first aspect, the Gf lens group is made of a plano-convex lens with a convex surface on the large conjugate side.
According to an eleventh aspect of the present invention, in the wide angle projection lens of the first aspect, the Gf lens group includes an aspheric surface.
According to a twelfth aspect of the present invention, the wide angle projection lens of the seventh aspect satisfies relations of the following expressions (9), (10), (11), (12), (13) and (14).
xcexd1 less than 41xe2x80x83xe2x80x83(9)
xcexd3 less than 31xe2x80x83xe2x80x83(10)
xcexd5 less than 32xe2x80x83xe2x80x83(11)
n1 greater than 1.54xe2x80x83xe2x80x83(12)
n3 greater than 1.65xe2x80x83xe2x80x83(13)
n5 greater than 1.65xe2x80x83xe2x80x83(14)
where
xcexd1: Abbe number in d line of vitreous material making up the first lens
xcexd3: Abbe number in d line of vitreous material making up the second lens
xcexd5: Abbe number in d line of vitreous material making up the third lens
n1: refractive index in d line of vitreous material making up the first lens
n3: refractive index in d line of vitreous material making up the second lens
n5: refractive index in d line of vitreous material making up the third lens.
According to a thirteenth aspect of the present invention, the wide angle projection lens of the seventh aspect satisfies relations of the following expressions (15), (16), (17), (18), (19) and (20).
xcexd15 less than 35xe2x80x83xe2x80x83(15)
xcexd19 less than 33xe2x80x83xe2x80x83(16)
xcexd20 greater than 50xe2x80x83xe2x80x83(17)
n15 greater than 1.60xe2x80x83xe2x80x83(18)
n19 greater than 1.65xe2x80x83xe2x80x83(19)
n20 less than 1.70xe2x80x83xe2x80x83(20)
where
xcexd15: Abbe number in d line of vitreous material making up the eighth lens
xcexd19: Abbe number in d line of vitreous material making up the tenth lens
xcexd20: Abbe number in d line of vitreous material making up the eleventh lens
n15: refractive index in d line of vitreous material making up the eighth lens
n19: refractive index in d line of vitreous material making up the tenth lens
n20: refractive index in d line of vitreous material making up the eleventh lens.
The present invention is also directed to a projection display device. According to a fourteenth aspect of the present invention, the projection display device comprises: a light source; a reflection light valve having an image display surface; illumination optical means leading an outgoing luminous flux from the light source to the reflection light valve; and the wide angle projection lens as defined in any one of the first to thirteenth aspects, enlargedly projecting a modulated luminous flux which is two-dimensionally modulated through reflection by the reflection light valve.
According to a fifteenth aspect of the present invention, in the projection display device of the fourteenth aspect, a lens closest to the reflection light valve among optical elements constituting the illumination optical means is a plano-convex lens, the plano-convex lens is disposed proximately to the image display surface of the reflection light valve, with its plane surface facing the same, and the plano-convex lens is also used as a Gf lens group closest to a small conjugate side among groups of lenses constituting the wide angle projection lens.
According to a sixteenth aspect of the present invention, in the projection display device of the fourteenth aspect, the intersection of the image display surface of the reflection light valve and an optical axis of the wide angle projection lens does not coincide with a center point of the image display surface.
According to a seventeenth aspect of the present invention, in the projection display device of the fifteenth aspect, the optical axis of the wide angle projection lens is parallel to a normal of the image display surface of the reflection light valve and an optical axis of lenses other than the plano-convex lens in the illumination optical means is tilted with respect to the normal of the image display surface of the reflection light valve.
According to an eighteenth aspect of the present invention, in the projection display device of the fourteenth aspect, the reflection light valve is a liquid crystal light valve.
According to a nineteenth aspect of the present invention, in the projection display device of the fourteenth aspect, the reflection light valve is made of a mirror array including a plurality of tiltable unit mirrors.
 less than Functions greater than 
The wide angle projection lens of these aspects of the present invention performs the following functions.
In the wide angle projection lens of the first aspect of the present invention, it is possible to achieve an image circle large enough for the off-axis projection system, ensure such a large air spacing as to avoid interference between the illumination optical system and the projection optical system and a small lens diameter of an incident part of the front group in the wide angle projection lens system and realize excellent optical properties such as low chromatic aberration, low distortion aberration and high resolution in spite of wide angle of view and short focal length.
Further, the conditional expressions (1) to (3) are intended to correct the aberration properties of the whole system well while ensuring a long back focal length in the Gnp lens group which is the front group of the projection lens system.
The conditional expression (1) defines the ratio of the focal length of the Gn lens group having negative refractive power among the Gnp lens group to the whole lens system. Over the upper limit of the conditional expression (1), though the retrofocus property of the Gnp lens group is enhanced and it is therefore advantageous to keep a long back focal length of the Gnp lens group, high-order off-axis aberrations such as astigmatism and coma aberration by the Gn lens group occur too greatly and therefore it becomes more difficult to realize excellent imaging properties. Below the lower limit of the conditional expression (1), it becomes more difficult to ensure a long back focal length of the Gnp lens group. Since it is necessary to ensure an unnecessary large space between the Gn lens group and the Gp lens group in order to ensure the long back focal length of the Gnp lens group, unpreferably, the total length of the whole lens system increases and accordingly the outer diameter of the Gn1 lens group which is the front group of the Gn lens group becomes larger.
The conditional expression (2) defines the ratio of the focal length of the Gp lens group having positive refractive power among the Gnp lens group to the whole lens system. Over the upper limit of the conditional expression (2), though it is advantageous to keep a long back focal length of the Gnp lens group, the focal length of the whole lens system becomes long and it becomes more difficult to ensure an necessary angle of view. Further, in order to satisfy the necessary angle of view, the negative power of the Gn lens group becomes great and it is therefore becomes more difficult to correct the off-axis aberration. Below the lower limit of the conditional expression (2), it becomes more difficult to ensure a long back focal length of the Gnp lens group.
The conditional expression (3) defines the ratio of the air spacing between the Gn lens group and the Gp lens group to the focal length of the whole lens system. Over the upper limit of the conditional expression (3), though it is advantageous to ensure a long back focal length of the Gnp lens group, the diameter of lens in the Gn lens group becomes large and the total length of the whole lens system becomes unnecessarily long. Below the lower limit of the conditional expression (3), it becomes more difficult to ensure a long back focal length of the Gnp lens group. Further, in order to satisfy the necessary angle of view, the negative power of the Gn lens group becomes great and it is therefore becomes more difficult to correct the off-axis aberration.
The conditional expression (4) defines the ratio of the focal lengths between the Gf lens group and the Gnp lens group. Over the upper limit of the conditional expression (4), though the air spacing between the Gnp lens group and the Gf lens group becomes large, the total length of the whole lens system becomes unnecessarily long and the diameter of lens on the incident side (light valve side) among the Gnp lens group becomes large when the necessary F number is ensured. Further, there arises necessity of ensuring an unnecessarily long back focal length of the Gnp lens group and it is therefore becomes more difficult to correct the off-axis aberration. Below the lower limit of the conditional expression (4), the air spacing between the Gnp lens group and the Gf lens group becomes small and an interference is thereby caused between the illumination optical system and the projection optical system, to raises a problem in ensuring the uniformity in luminance distribution of the projection image.
The wide angle projection lens of the second aspect of the present invention can ensure an appropriate back focal length of the Gnp lens group and realize excellent imaging properties. The conditional expression (5) defines the ratio of the back focal length and the focal length of the Gnp lens group. Over the upper limit of the conditional expression (5), though a long back focal length can be ensured and it is therefore advantageous to avoid the interference between the illumination optical system and the projection optical system, there arises necessity of ensuring an unnecessarily long back focal length of the Gnp lens group and therefore correction of the off-axis aberration especially becomes more difficult, to cause deterioration in resolution of lens system.
Below the lower limit of the conditional expression (5), the back focal length of the Gnp lens group becomes short and the interference between the illumination optical system and the projection optical system raises a problem in ensuring the uniformity in luminance distribution of the projection image.
The wide angle projection lens of the third aspect of the present invention can reduce the diameter of the lens on the light valve side (the small conjugate side of the whole lens system) among the Gnp lens group and avoid the interference between the illumination optical system and the projection optical system. The conditional expression (6) defines the ratio between the absolute value of the pupil distance on the small conjugate side viewed from the last surface of the small conjugate side and the focal length of the Gnp lens group. Over the upper limit of the conditional expression (6), the pupil distance is too far from the last surface of the Gnp lens group and the diameter of lens on the light valve side becomes large and an interference is thereby caused between the illumination optical system and the projection optical system, to raise a problem such as deterioration of uniformity in luminance distribution of the projection image.
The wide angle projection lens of the fourth aspect of the present invention can ensure an appropriate air spacing between the Gp lens group and the Gf lens group, avoid the interference between the illumination optical system and the projection optical system and realize excellent imaging properties. The conditional expression (7) defines the ratio between the air spacing between the Gp lens group and the Gf lens group and the focal length of the Gf lens group. Over the upper limit of the conditional expression (7), though a large air spacing can be ensured and it is therefore advantageous to avoid the interference between the illumination optical system and the projection optical system, there arises necessity of ensuring an unnecessarily long back focal length of the Gnp lens group and therefore correction of the off-axis aberration especially becomes more difficult, to cause deterioration in resolution of the lens system. Below the lower limit of the conditional expression (7), the air spacing becomes too small and an interference is thereby caused between the illumination optical system and the projection optical system, to raise a problem such as deterioration of uniformity in luminance distribution of the projection image.
The wide angle projection lens of the fifth aspect of the present invention can ensure an appropriate distance from the Gf lens group to the pupil on the small conjugate side of the Gnp lens group, avoid the interference between the illumination optical system and the projection optical system, realize excellent imaging properties and couple the reflection light from the light valve onto the projection lens system with high efficiency. The conditional expression (8) defines the ratio between the distance from the Gf lens group and the pupil on the small conjugate side of the Gnp lens group and the focal length of the Gf lens group. Over the upper limit of the conditional expression (8), the reflection light from the light valve is condensed at a point closer to the light valve off from the pupil on the small conjugate side of the Gnp lens group and the efficiency in imaging of the reflection light onto the Gnp lens group is thereby lowered and the uniformity in luminance distribution of the projection image in the off-axis projection system is deteriorated. Below the lower limit of the conditional expression (8), the reflection light from the light valve is condensed at a point closer to the screen off from the pupil on the small conjugate side of the Gnp lens group and the efficiency in imaging of the reflection light onto the Gnp lens group is thereby lowered and the uniformity in luminance distribution of the projection image in the off-axis projection system is deteriorated. Further, since the air spacing between the Gf lens group and the Gnp lens group becomes small, an interference is thereby caused between the illumination optical system and the projection optical system, to deteriorate the uniformity in luminance distribution of the projection image.
In the wide angle projection lens of the sixth aspect of the present invention, since the Gn lens group comprises two groups of lenses, i.e., the Gn1 lens group and the Gn2 lens group and the Gp lens group comprises two groups of lenses, i.e., the Gp1 lens group and the Gp2 lens group, the constitution of the Gnp lens group having a long back focal length is made clearer and it is possible to easily provide a lens system to realize the basic specifications relating to (1) wide angle of view, (2) small diameter of a lens on the incident side, (3) long back focal length and (4) large image circle and the basic properties of (a) low chromatic aberration, (b) low distortion aberration and (c) high resolution, attaining the objects of the present invention.
In the wide angle projection lens of the seventh aspect of the present invention, the shape and the sign of refractive power (positive or negative) of the single lenses constituting the Gn1 lens group, the Gn2 lens group or the Gp1 lens group are made clear. As a result, it is possible to provide a specific constitution of a wide angle projection lens which has an image circle large enough for the off-axis projection system, ensures such a large air spacing as to avoid the interference between the illumination optical system and the projection optical system and has excellent optical properties such as low chromatic aberration, low distortion aberration and high resolution in spite of wide angle of view and short focal length.
In the wide angle projection lens of the eighth aspect of the present invention, since the Gp2 lens group includes an aspheric surface, especially high-order spherical aberration can be corrected strongly, to realize excellent imaging properties.
In the wide angle projection lens of the ninth aspect of the present invention, since the Gp2 lens group includes the stop means, it is possible to reduce the diameter of the lens on the small conjugate side among the Gnp lens group, prevent the interference between the illumination optical system and the projection optical system and improve the uniformity in luminance distribution of the projection image in the projection display device of off-axis projection system.
In the wide angle projection lens of the tenth aspect of the present invention, since the Gf lens group is a plano-convex lens and disposed with its plane surface facing the light valve side, it is possible to couple the reflection luminous flux from the light valve onto the Gnp lens group with high efficiency. Further, by facing the plane surface of the plano-convex lens toward the light valve, it becomes easier to set the relative positions of the Gf lens group and the light valve.
In the wide angle projection lens of the eleventh aspect of the present invention, since the Gf lens group includes an aspheric surface, high-order off-axis aberrations such as distortion aberration, coma aberration and astigmatism can be corrected strongly, to realize excellent imaging properties.
In the wide angle projection lens of the twelfth aspect of the present invention, by limiting the conditions of refractive index and Abbe number of the first to third lenses in the Gn1 lens group, an excellent correction of chromatic aberration is realized. The conditional expressions (9), (10) and (11) define the upper limits of Abbe number in the d lines of the respective vitreous materials making up the first lens, the second lens and the third lens. The conditional expression (12), (13) and (14) define the lower limits of refractive index in the d lines of the respective vitreous materials making up the first lens, the second lens and the third lens. Over the upper limits of the conditional expressions (9), (10) and (11), it becomes more difficult to correct the chromatic aberration of the whole lens system. Also below the lower limits of the conditional expressions (12), (13) and (14), it becomes more difficult to correct the chromatic aberration of the whole lens system.
In the wide angle projection lens of the thirteenth aspect of the present invention, by limiting the conditions of refractive index and Abbe number of the eighth, tenth and eleventh lenses in the Gp1 lens group, an excellent correction of chromatic aberration is realized. The conditional expressions (15) and (16) define the upper limits of Abbe number in the d lines of the respective vitreous materials making up the eighth lens and the tenth lens, and the conditional expression (17) defines the lower limit of Abbe number in the d line of the vitreous material making up the eleventh lens. The conditional expressions (18) and (19) define the lower limits of refractive index in the d lines of the respective vitreous materials making up the eighth lens and the tenth lens, and the conditional expression (20) defines the upper limit of refractive index in the d line of the vitreous material making up the eleventh lens. Over the upper limits of the conditional expressions (15), (16) and (20), it becomes more difficult to correct the chromatic aberration of the whole lens system. Also below the lower limits of the conditional expressions (17), (18) and (19), it becomes more difficult to correct the chromatic aberration of the whole lens system.
According to the fourteenth aspect of the present invention, it is possible to achieve a small-size, high-quality and low-cost projection display device mounted with the wide angle projection lens of any one of the first to thirteenth aspects.
According to the fifteenth aspect of the present invention, by disposing a plano-convex lens near the light valve, it is possible to achieve a projection display device capable of efficiently transmitting the luminous flux from the illumination optical system to the projection optical system. Further, by facing the plane surface of the plano-convex lens toward the light valve, it becomes easier to set the relative positions of the Gf lens group and the light valve.
According to the sixteenth aspect of the present invention, since a device of off-axis projection system in which the intersection between the image display surface and the optical axis of the projection lens is displaced from the center point of the image display surface is obtained, the interference between the illumination optical system and the projection optical system can be prevented by utilizing the property of large image circle of the wide angle projection lens as defined in any one of the first to thirteenth aspects.
In the projection display device of the seventeenth aspect of the present invention, by setting the normal of the image display surface of the light valve and the optical axis of the projection lens parallel to each other, the distortion of the projection image can be controlled within the limits of designed distortion aberration. Further, since the optical axis of lenses other than the plano-convex lens near the light valve among the illumination optical system is tilted with respect to the normal of the image display surface of the light valve, the interference between the illumination optical system and the projection optical system can be prevented.
According to the eighteenth aspect of the present invention, it is possible to achieve a small-size, high-quality and low-cost projection display device mounted with a liquid crystal light valve.
According to the nineteenth aspect of the present invention, it is possible to achieve a small-size, high-quality and low-cost projection display device mounted with a light valve having a movable micromirror array, such as DMD.
 less than Effects greater than 
The wide angle projection lens of the first aspect of the present invention comprises the Gnp lens group having positive refractive power and the Gf lens group having positive refractive power in the order from the large conjugate side toward the small conjugate side and the Gnp lens group comprises the Gn lens group having negative refractive power and the Gp lens group having positive refractive power in the order from the large conjugate side toward the small conjugate side, and in this wide angle projection lens of the first aspect, the conditional expressions (1) to (3) define conditions for ensuring a long back focal length in the Gnp lens group which is the front group of the projection lens system while correcting the aberration properties of the whole system well and the conditional expression (4) defines the ratio of focal lengths between the Gf lens group and the Gnp lens group. As a result, a wide angle projection lens which has an image circle large enough for the off-axis projection system, ensures such a large air spacing as to avoid the interference between the illumination optical system and the projection optical system and a small diameter of lens in an incident part of the front group in the wide angle projection lens system and has excellent optical properties such as low chromatic aberration, low distortion aberration and high resolution in spite of wide angle of view and short focal length.
The wide angle projection lens of the second aspect of the present invention can ensure an appropriate back focal length of the Gnp lens group and realize excellent imaging properties of the whole lens system by defining the ratio of the back focal length and the focal length of the Gnp lens group by the conditional expression (5).
The wide angle projection lens of the third aspect of the present invention can reduce the diameter of the lens on the light valve side (the small conjugate side of the whole lens system) among the Gnp lens group and avoid the interference between the illumination optical system and the projection optical system by defining the ratio between the absolute value of the pupil distance on the small conjugate side of the Gnp lens group viewed from the last surface of the small conjugate side and the focal length of the Gnp lens group by the conditional expression (6). As a result, it becomes possible to enhance the uniformity in luminance distribution of a display image of the projection display device using the wide angle projection lens.
The wide angle projection lens of the fourth aspect of the present invention can ensure an appropriate air spacing between the Gp lens group and the Gf lens group, avoid the interference between the illumination optical system and the projection optical system to enhance the uniformity in luminance distribution of the projection image, and realize excellent imaging properties by defining the ratio between the air spacing between the Gp lens group and the Gf lens group and the focal length of the Gf lens group by the conditional expression (7).
The wide angle projection lens of the fifth aspect of the present invention can ensure an appropriate distance from the Gf lens group to the pupil of the Gnp lens group on the small conjugate side, avoid the interference between the illumination optical system and the projection optical system to enhance the uniformity in luminance distribution of the projection image, realize excellent imaging properties, and couple the reflection light from the light valve onto the projection lens system with high efficiency by defining the ratio between the distance from the Gf lens group and the pupil of the Gnp lens group on the small conjugate side and the focal length of the Gf lens group by the conditional expression (8).
In the wide angle projection lens of the sixth aspect of the present invention, since the Gn lens group which is a constituent of the Gnp lens group comprises two groups of lenses, i.e., the Gn1 lens group and the Gn2 lens group and the Gp lens group which is a constituent of the Gnp lens group comprises two groups of lenses, i.e., the Gp1 lens group and the Gp2 lens group, the constitution of the Gnp lens group having a large back focal length can be achieved and it is possible to achieve an image circle large enough for the off-axis projection system, ensure such a large air spacing as to avoid the interference between the illumination optical system and the projection optical system and a small diameter of lens in an incident part of the front group in the wide angle projection lens system and realize excellent optical properties such as low chromatic aberration, low distortion aberration and high resolution in spite of wide angle of view and short focal length.
In the wide angle projection lens of the seventh aspect of the present invention, a specific constitution of the single lenses constituting the Gn1 lens group, the Gn2 lens group or the Gp1 lens group on their shape and sign of refractive power (positive or negative) is made clear. As a result, it is possible to provide a wide angle projection lens which has an image circle large enough for the off-axis projection system, ensures such a large air spacing as to avoid the interference between the illumination optical system and the projection optical system and a small diameter of lens in an incident part of the front group in the wide angle projection lens system and has excellent optical properties such as low chromatic aberration, low distortion aberration and high resolution in spite of wide angle of view and short focal length.
In the wide angle projection lens of the eighth aspect of the present invention, since the Gp2 lens group includes an aspheric surface, especially high-order spherical aberration can be corrected strongly, to realize excellent imaging properties.
In the wide angle projection lens of the ninth aspect of the present invention, since the Gp2 lens group closest to the light valve side among the Gnp lens group includes the stop means, it is possible to reduce the diameter of the lens on the small conjugate side among the Gnp lens group, prevent the interference between the illumination optical system and the projection optical system and improve the uniformity in luminance distribution of the projection image in the projection display device of off-axis projection system.
In the wide angle projection lens of the tenth aspect of the present invention, since the Gf lens group is a plano-convex lens and disposed with its plane surface facing the light valve side, it is possible to couple the reflection luminous flux from the light valve onto the Gnp lens group with high efficiency. Further, by facing the plane surface of the plano-convex lens toward the light valve, it becomes easier to set the relative positions of the Gf lens group and the light valve.
In the wide angle projection lens of the eleventh aspect of the present invention, since the Gf lens group includes an aspheric surface, high-order off-axis aberrations such as distortion aberration, coma aberration and astigmatism can be corrected strongly, to realize excellent imaging properties.
In the wide angle projection lens of the twelfth aspect of the present invention, since the Abbe numbers of the respective vitreous materials making up the first lens, the second lens and the third lens are defined by the conditional expressions (9), (10) and (11) and the refractive indices of the respective vitreous materials making up the first lens, the second lens and the third lens are defined by the conditional expressions (12), (13) and (14), it is possible to achieve a wide angle projection lens with chromatic aberration well corrected.
In the wide angle projection lens of the thirteenth aspect of the present invention, since the Abbe numbers of the respective vitreous materials making up the eighth lens, the tenth lens and the eleventh lens are defined by the conditional expressions (15), (16) and (17) and the refractive indices of the respective vitreous materials making up the eighth lens, the tenth lens and the eleventh lens are defined by the conditional expressions (18), (19) and (20), it is possible to achieve a wide angle projection lens with chromatic aberration well corrected.
According to the fourteenth aspect of the present invention, it is possible to achieve a small-size, high-quality and low-cost projection display device mounted with the wide angle projection lens of any one of the first to thirteenth aspects.
According to the fifteenth aspect of the present invention, by disposing a plano-convex lens near the light valve, it is possible to achieve a projection display device capable of efficiently transmitting the luminous flux from the illumination optical system, being reflected by the light valve and entering the projection optical system. Further, by facing the plane surface of the plano-convex lens toward the light valve, it becomes easier to set the relative positions of the Gf lens group and the light valve.
According to the sixteenth aspect of the present invention, since a device of off-axis projection system in which the intersection between the image display surface and the optical axis of the projection lens is displaced from the center point of the image display surface is obtained, it is possible to provide a projection display device which can avoid the interference between the illumination optical system and the projection optical system by utilizing the property of large image circle of the wide angle projection lens as defined in any one of the first to thirteenth aspects and can achieve a display image with uniform luminance distribution.
In the projection display device of the seventeenth aspect of the present invention, by setting the normal of the image display surface of the light valve and the optical axis of the projection lens parallel to each other, the distortion of the projection image can be controlled within the limits of designed distortion aberration. Further, since the optical axis of lenses other than the plano-convex lens near the light valve among the illumination optical system is tilted with respect to the normal of the image display surface of the light valve, the interference between the illumination optical system and the projection optical system can be avoided, to enhance the uniformity in luminance distribution of the display image.
According to the eighteenth aspect of the present invention, it is possible to achieve a small-size, high-quality and low-cost projection display device mounted with a liquid crystal light valve as the light valve.
According to the nineteenth aspect of the present invention, it is possible to achieve a small-size, high-quality and low-cost projection display device mounted with a light valve having a movable micromirror array, such as DMD, as the light valve.
The present invention relates to a projection lens mounted in a projection display device using a reflection liquid crystal panel and a DMD and the like as a light valve and an object of the present invention is to provide a projection lens achieving projection with wide angle of view, having a small diameter of lens on the incident side and a long back focal length to avoid an interference between the illumination optical system and the projection optical system in an off-axis projection optical system and having a large image circle required for off-axis projection.
Another object of the present invention is to provide a wide angle projection lens for a low-cost rear projection type display device achieving high-quality image projection, by satisfying the early-discussed specifications for (1) wide angle of view, (2) small diameter of a lens on the incident side, (3) long back focal length and (4) large image circle and achieving the early-discussed fundamental properties for resolving the problems, i.e., (a) low chromatic aberration, (b) low distortion aberration and (c) high resolution. A still another object of the present invention is to provide a high-quality, low-cost and small-size projection display device using the wide angle projection lens.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.